The present invention relates to an improved exercise device for the upper body muscles that provides an upward, vertical force to assist the exerciser with chin-ups and dips. Chin-up or dip exercises require strong upper body muscles. In most exercisers these upper body muscles are not sufficiently developed and the exercises can only be performed with great difficulty if at all.
Typical upper body exercise apparatuses either provide no assistance to the exerciser or are cumbersome to use and operate. For example, the device described in the patent to Roberts, U.S. Pat. No. 4,111,414, requires the user to step into a harness while manually adjusting weights. Other devices provide a platform on which the exerciser stands, but the force applied to assist the exerciser either causes arcuate motion of the platform, or provides a non-linear assist force.
In particular, McFee in U.S. Pat. No. 4,470,587, illustrates an oscillating platform articulated to a parallelogram assembly having fixed pivot points. Thus, as the platform moves from an initial position to an upper position, the platform must necessarily traverse an arc. The arcuate motion of the platform causes the user's feet to traverse an arc while the user's hands grip the chin-up or dip handles and a true chin-up or dip exercise cannot be performed.
The Martin device, U.S. Pat. No. 4,452,447, contains an oscillating platform attached to elastic spring members which provide an upward force to assist the user. The elastic members behave in a similar fashion to springs and the amount of assistance force therefore varies with the displacement of the platform.
One device described in Potts U.S. Pat. No. 4,846,458, does disclose an oscillating platform with essentially uniform upward force and free of arcuate motion. The Potts device uses a system of levers and hydraulic lifts to move the platform. As the platform moves up and down, a short arm causes the effective length of the moment arm to change. The change in moment arm compensates for the non-linearity of the pneumatic lifters and provides a substantially linear assist force to the platform. An accumulator and air compressor motor are used to control the volume of fluid in the pneumatic cylinder and thus the amount of assist provided to the user.